Google has replaced its logo with a time-lapse animation of blooming flowers to mark Earth Day, a worldwide series of events held annually to raise ecological awareness.

The latest in the search engine's so-called doodles sees purple, red and yellow flowers sprout from a series of shrubs laid out to spell Google.

Earth Day was first held on 1970 after Gaylord Nelson, a US senator, conceived it as a tool to promote an environmental agenda after witnessing a huge oil spill off the coast of California a year earlier.

Organisers claim the 1970 event rallied millions across the country as it tapped in to the rise of hippie culture and anti-Vietnam war protest movements. "Groups that had been fighting against oil spills, polluting factories and power plants, raw sewage, toxic dumps, pesticides, freeways, the loss of wilderness, and the extinction of wildlife suddenly realised they shared common values," the official Earth Day website says.

Major Earth Day events have been held in subsequent years, always on 22 April – the same date as the original event. In 1990 the event went global for the first time with activities involving an estimated 200 million people in 141 countries. The day's 30th anniversary in 2000 was used to promote a global call for cleaner energy while 2010 saw the launch an initiative to plant 1m trees.

This year's Earth Day is centred around a scheme called "one billion acts of green", which encourages individuals to make simple environmentally conscious pledges, such as switching off lightbulbs or reducing car journeys. Organisers say the day is now observed in 192 countries.